The present invention relates to an optical display apparatus for displaying image information and character information.
In recent years, an optical display apparatus for displaying image information and character information has been used in various fields. An example of such an optical display apparatus is an electronic optical display apparatus widely used in a traffic information display board, a direction board or a billboard. Related techniques are disclosed in, for example, Japanese Laid-Open Publication Nos. 6-228921, 7-129108, 7-140912, 8-6513, 8-158322, 8-160894, etc. First, one of the most typical examples of such an optical display apparatus, an optical traffic sign incorporating a fluorescent lamp therein, will be described below with reference to the figures. However, various other conventional structures are known in the art, such as those incorporating an LED or an EL device for producing a self-luminous display, and those using an optical fiber or a light guide plate for guiding light from a light source.
FIG. 1A is a side view illustrating a structure of a conventional optical traffic sign, and FIG. 1B is a front view illustrating the same. Specifically, reference numeral 156 denotes a sign display board, 157 a ring-shaped fluorescent tube, 158 a sign body, and 159 a sign pole.
The sign display board 156 includes a semi-transparent resin on which a sign pattern is printed. The sign can be recognized even at night by illuminating the pattern from the inside of the sign with light from the ring-shaped fluorescent tube 157. The sign body 158, supporting the ring-shaped fluorescent tube 157 and the sign display board 156, is installed on a side wall beside a road or on a tunnel ceiling by being supported by the sign pole 159.
However, the above-described conventional structure has the following problems.
First, since the sign pattern is either printed on the semi-transparent resin or is made of a color resin, a large portion of light emitted by the ring-shaped fluorescent tube 157, as a light source, is absorbed by the resin, whereby the display is not sufficiently bright.
Second, since the display section, including the sign display board 156 and the fluorescent tube (light source) 157, is supported by the sign body 158, the portion including the display section is large and heavy. Moreover, since the sign pole 159 supporting the same must also be robust, the overall structure is even larger and heavier.
Third, the structure must be installed so that it substantially projects from the installation surface, i.e., a road side wall or a tunnel ceiling. Therefore, it may be hit for some reasons by a moving object such as a person, a car or a load, thereby damaging the display apparatus body while also damaging the moving object. To avoid such an accident requires a large installation space, which is not economical.
The above-described problems arise not only from the optical traffic sign incorporating a fluorescent lamp therein, illustrated in FIGS. 1A and 1B as a conventional example, but also from those of a self-luminous type such as an LED or those using an optical fiber or a light guide plate for guiding light from the light source. Moreover, the problems are not limited to the above-described traffic sign, but are common to a general class of optical display apparatuses where a pattern to be displayed is illuminated with light from a light source.
Those using a hologram are possible alternatives which may solve the above-described problems.
First, a principle of producing a hologram based on a commonly-employed conventional technique and a principle of displaying (reconstructing) image information using such a conventional hologram will be described below.
FIG. 2A is a diagram schematically illustrating a typically-employed principle of producing a hologram.
In particular, an object O is illuminated with object illumination light IL emitted from a laser light source, thereby forming object light OL having information relating to the shape, etc., of the object O, and making the object light OL be incident upon a hologram dry plate H1. At the same time, reference light RL1, formed by splitting light emitted from the same laser light source as the object illumination light IL by means of a beam splitter, or the like, is directed to be incident upon the hologram dry plate H1 from an inclined direction. Thus, interference fringes between the object light OL and the reference light RL1 are recorded on the hologram dry plate H1. The hologram dry plate H1 on which such interference fringes (having information of the object O) are recorded will hereinafter be referred to also as the xe2x80x9chologram plate H1xe2x80x9d.
FIG. 2B is a diagram schematically illustrating a principle of reconstructing the hologram plate H1 which is provided according to FIG. 2A.
In particular, the reconstruction illumination light RI1, which is light from the same laser light source as that used for producing the hologram plate H1, is directed to propagate through the same path as that for the reference light RL1 (see FIG. 2A) so as to irradiate the hologram plate H1. Thus, light (reconstruction light) R1, having information of the object recorded on the hologram plate H1, is reconstructed, so that a reconstructed image I1 is observed at a position where the object was originally located.
The above-described method, however, requires the use of a laser light source as a light source when producing and reconstructing the hologram plate H1, and thus has such problems that the cost cannot be reduced and the handling thereof is complicated.
On the other hand, in a reflection-type hologram to be described below, a hologram image can be reconstructed using white light.
To produce a reflection-type hologram, the hologram plate H1 is first produced by the method as illustrated in FIG. 2A, and then irradiated with reconstruction illumination light (laser light) RI21, as illustrated in FIG. 3A, in a direction opposite to that of the reconstruction illumination light RI1 illustrated in FIG. 2B. Thus, reconstruction light R21, directed from the hologram plate H1 to the position where the object was located, is reconstructed, thereby reconstructing a real image (reconstructed image) I21 of the object at a position where the object was located. Then, a new hologram dry plate H2 is placed at a position spaced apart from the reconstructed image I21 of the object by a distance Z0, as illustrated in FIG. 3B, and reference light RL2 is directed to be incident upon the hologram dry plate H2 from an inclined direction opposite from the hologram plate H1. The reference light RL2 is formed by splitting light emitted from the same laser light source as the reconstruction illumination light RI21 by means of a beam splitter, or the like. Thus, interference fringes between the reconstruction illumination light RI21 and the reference light RL2 are recorded on the hologram dry plate H2. The hologram dry plate H2 on which such interference fringes (having information of the object) are recorded as a reflection-type hologram will hereinafter be referred to also as the xe2x80x9creflection-type hologram plate H2xe2x80x9d.
FIG. 3C is a diagram schematically illustrating a principle of reconstructing the reflection-type hologram plate H2 formed as described above.
In particular, the reflection-type hologram plate H2 is irradiated with reconstruction illumination light RI22 (white light from a point light source spaced apart from the reflection-type hologram plate H2 by a certain distance) which propagates in a direction diametrically opposite to that of the reference light RL2 illustrated in FIG. 3B. Thus, reconstruction light R22 having information of the object recorded on the reflection-type hologram plate H2 is reconstructed so as to form a reconstructed image I22 at a position where the object was originally located.
In a reflection-type hologram, a wavelength selectivity (color selectivity) in the optical diffraction characteristic (the diffraction efficiency) is high. Therefore, the image I22 is reconstructed by light having a wavelength close to that of the laser light used for producing the hologram. Thus, a color image can also be reconstructed by superposition. However, a clear reconstructed image cannot be obtained when the distance z0 between the position of the reflection-type hologram plate H2 and a position where the reconstructed image I22 is displayed is large.
The reason why a reconstructed image of the reflection-type hologram is blurred will further be described with reference to FIGS. 3D and 3E.
The reconstruction illumination light RI22 directed toward the reflection-type hologram is white light. Therefore, wavelengths other than a wavelength xcex0 of the laser light used to produce the hologram are also contained in the reconstruction illumination light RI22. A reflection-type hologram has a high wavelength selectivity, as shown in a graph of FIG. 3E illustrating the wavelength dependency of the diffraction efficiency, whereby substantially none of light having a wavelength far away from the wavelength (center wave length) xcex0 of the laser light used to produce the hologram is diffracted. Therefore, only light having a wavelength close to the center wavelength xcex0 is diffracted, thereby reconstructing the image I22. In practice, however, light having a wavelength which is close to, but different from, the center wavelength xcex0, as represented by xcex1 and xcex2 in FIGS. 3D and 3E, is also contained in the reconstructed light R22, thereby also forming and superimposing reconstructed images from such light on the intended reconstructed image from the light having the center wavelength xcex0. By this effect, the reconstructed image I22 is blurred when the distance z0 to the position where the image I22 is formed is set to be large. That is, with a reflection-type hologram, a clear reconstructed image I22 cannot be viewed when it is viewed from a distance greater than the distance z0 set when producing the hologram. This can be a very critical disadvantage in an application, such as an optical information apparatus, e.g., a traffic sign, which aims to clearly transfer prescribed information.
As described above, the commonly-employed conventional hologram and the reflection-type hologram using the same have significant problems to be solved, in terms of the cost, the accurate display/transfer of information, etc., before they can be used in an optical display apparatus such as a traffic sign, for example.
A hologram display method different from those described above is what is known as a rainbow hologram.
To produce a rainbow hologram, the hologram plate H1 is first produced by the method as illustrated in FIG. 2A, which is then irradiated with reconstruction illumination light (laser light) RI31 in a direction opposite to that of the reconstruction illumination light RI1 illustrated in FIG. 2B and through a slit having a width of xcex94, as illustrated in FIG. 4A. Thus, reconstruction light R31, directed from the hologram plate H1 to the position where the object was located, is reconstructed, thereby reconstructing a real image (reconstructed image) I31 of the object at a position where the object was located. Then, a new hologram dry plate H3 is placed at a position spaced apart from the reconstructed image I31 of the object by a distance Z0, as illustrated in FIG. 4B, and reference light RL3 is directed to be incident upon the hologram dry plate H3 from an inclined direction as that for the hologram plate H1. The reference light RL3 is formed by splitting light emitted from the same laser light source as the reconstruction illumination light RI31 by means of a beam splitter, or the like. Thus, interference fringes between the reconstruction illumination light RI31 and the reference light RL3 are recorded on the hologram dry plate H3. The hologram dry plate on which such interference fringes (having information of the object) are recorded as a transmission-type hologram by the rainbow hologram method will hereinafter be referred to also as the xe2x80x9crainbow hologram plate H3xe2x80x9d.
FIG. 4C is a diagram schematically illustrating a principle of reconstructing the rainbow hologram plate H3 formed as described above.
In particular, the rainbow hologram plate H3 is irradiated with reconstruction illumination light RI32 (white light from a point light source spaced apart from the rainbow hologram plate H3 by a certain distance) which propagates in a direction diametrically opposite to that of the reference light RL3 illustrated in FIG. 4B. Thus, reconstruction light R32 having information of the object recorded on the rainbow hologram plate H3 is reconstructed and directed toward the position where the slit was located during the hologram production, so as to form a reconstructed image I32 at a position where the object was originally located.
With a rainbow hologram formed as described above, a clearer reconstructed image is observed as compared to that observed by a reflection-type hologram. The reason for this will be described with reference to FIGS. 4D and 4E.
The reconstruction illumination light RI32 directed toward the rainbow hologram is white light. Therefore, wavelengths other than a wavelength xcex0 of the laser light used to produce the hologram are also contained in the reconstruction illumination light RI32. However, a rainbow hologram, which is a transmission-type hologram, has a low wavelength selectivity, as shown in a graph of FIG. 4E illustrating the wavelength dependency of the diffraction efficiency, whereby a relatively wide range of wavelengths are diffracted to emit the reconstruction light R32, thereby reconstructing the images I32 respectively corresponding to different wavelengths of light. However, since a slit is used when producing the rainbow hologram, the reconstructed images formed by the different wavelengths of light are formed at respectively different positions (i.e., spatially separated from one another). For example, reconstructed images formed by light having wavelengths which are different from the center wavelength xcex0, as represented by xcex1 and xcex2 in FIGS. 4D and 4E, are formed concurrently at positions different from that of the reconstructed image formed by light having the center wavelength xcex0, but are not spatially superimposed on the intended reconstructed image formed by the light having the center wavelength xcex0. Therefore, with the rainbow hologram, the reconstructed image I32 is relatively clearly observed, with the color of the image I32 changing as the observation position changes.
The phenomenon that the reconstructed image I32 is observed with different colors depending upon the observation position is where the nomenclature xe2x80x9crainbow hologramxe2x80x9d comes from, and various applications have been proposed in the art which take advantage of the phenomenon. However, in view of reconstructing a color image, on the other hand, such a change in the color of the reconstructed image I32 depending upon the observation position presents a disadvantage that a prescribed color image cannot be reconstructed. For example, in the case of the traffic sign as described above, use of a predetermined color also constitutes a part of the information to be transferred. Therefore, the above-described characteristic of the rainbow hologram presents a very critical disadvantage in the application thereof to an optical information apparatus aims to clearly transfer prescribed information.
The present invention has been made in view of the above-described problems existing in the prior art, and has an objective of providing a light-weight optical display apparatus which occupies a small space and is capable of reconstructing/displaying image information in a bright and clear manner, by using a hologram technique based on a novel method.
An optical display apparatus provided by one aspect of the present invention includes a hologram device and a light source. The hologram is a reflection-type hologram formed by: light having information of an object which is obtained by using light having passed through a slit; and reference light having an incident optical path different from that of the light having the information of the object, wherein a reconstructed image of the object is displayed by light from the light source. The above-described object is accomplished by such a feature.
In one embodiment, the light having the information of the object is object light which is obtained by irradiating the object with diffused light having passed through the slit. The diffused light may be formed by passing light through a ground glass.
In another embodiment, the light having the information of the object is reconstructed light obtained by reconstructing a transmission-type hologram which is formed by: object light obtained by irradiating the object with diffused light having passed through the slit; and irradiation light having an incident optical path different from that of the object light. The diffused light may be formed by passing light through a ground glass.
In still another embodiment, the light having the information of the object is reconstructed light of a transmission-type hologram which is obtained by passing through the slit which is arranged to be adjacent to the transmission-type hologram on which an image of the object is recorded.
In still another embodiment, the light having the information of the object is reconstructed light of a transmission-type hologram which is obtained by passing through: the slit which is arranged to be adjacent to the transmission-type hologram on which an image of the object is recorded; and a cylindrical lens having its generatrix along a longitudinal direction of the slit.
The reference light is provided by superposing a plurality of beams on one another in a direction orthogonal to a longitudinal direction of the slit.
Preferably, the light source is a linear light source. The linear light source may be arranged on or in a vicinity of a plane orthogonal to a longitudinal direction of the slit.
In one embodiment, an incident plane of the reference light is a plane orthogonal to a longitudinal direction of the slit. Alternatively, an incident plane of the reference light may be a plane different from a plane orthogonal to a longitudinal direction of the slit.
An optical display apparatus provided by another aspect of the present invention is an optical display apparatus including a hologram device and a light source. The hologram is a reflection-type hologram formed by: light having information of an object which is obtained by using diffused light diffusing in one direction; and reference light having an incident optical path different from that of the light having the information of the object, wherein a reconstructed image of the object is displayed by light from the light source. The above-described object is accomplished by such a feature.
In one embodiment, the light having the information of the object is object light which is obtained by irradiating the object with the diffused light.
In another embodiment, the light having the information of the object is reconstructed light obtained by reconstructing a transmission-type hologram which is formed by: object light obtained by irradiating the object with the diffused light; and irradiation light having an incident optical path different from that of the object light.
The reference light may be provided by superposing a plurality of beams on one another in a direction orthogonal to the direction in which the diffused light diffuses.
In still another embodiment, the light having the information of the object is reconstructed light of a transmission-type hologram which is obtained by passing through the slit which is arranged to be adjacent to the transmission-type hologram on which an image of the object is recorded. The reference light may be provided by superposing a plurality of beams on one another in a direction orthogonal to the direction in which the diffused light diffuses.
In one embodiment, the diffused light is formed by passing light through a lenticular lens.
Preferably, the light source is a linear light source. the linear light source may be arranged on or in a vicinity of a plane orthogonal to the direction in which the diffused light diffuses.
In one embodiment, an incident plane of the reference light is a plane orthogonal to the direction in which the diffused light diffuses. Alternatively, an incident plane of the reference light may be a plane different from a plane orthogonal to the direction in which the diffused light diffuses.
According to the present invention, there is provided an optical display system having a plurality of display units arranged on an arrangement plane in which reconstructed images from the plurality of units are synthesized and displayed, wherein each of the plurality of units is an optical display apparatus of the present invention having the above-described feature.
The hologram device in the optical display apparatus of the present invention may be provided by combining a plurality of hologram elements with one another.
The hologram device in the optical display apparatus of the present invention may be formed on a flexible substrate.
The hologram device in the optical display apparatus of the present invention may be portable.
The light source in the optical display apparatus of the present invention may be a linear light source; and a length and an installation direction of the linear light source may be set so that a predetermined reconstructed image viewing range is obtained.
The light source in the optical display apparatus of the present invention may be a linear light source; and a position where a reconstructed image is formed may be shifted by moving the linear light source out of an incident plane.
In some cases, the optical display apparatus of the present invention includes a plurality of the hologram devices, wherein the plurality of hologram devices are reconstructed by one light source.
The light source in the optical display apparatus of the present invention may be a linear light source. In some cases, the linear light source is a fluorescent lamp or a combination of a fluorescent lamp and a reflecting plate.
The light source in the optical display apparatus of the present invention may be a linear light source including a polygon mirror and a point light source.
The light source in the optical display apparatus of the present invention may be a linear light source which is a linear light source comprising a cylindrical mirror and a point light source.
The light source in the optical display apparatus of the present invention may be a linear light source configured by a light beam which is linearly focused by a mirror or a lens.
The light source in the optical display apparatus of the present invention may be a linear light source including an array of point light sources.
The light source in the optical display apparatus of the present invention may be a linear light source configured by a bright line displayed on a two-dimensional display apparatus.
According to the present invention, there may be provided an optical display system, including an optical display apparatus of the present invention having the above-described feature and an information communication apparatus. The optical display apparatus may three-dimensionally display a communication area of the information communication apparatus. A display area of the optical display apparatus and the communication area of the information communication apparatus may match with each other. The information communication apparatus may perform a one-way communication or an interactive communication of information.
An optical display apparatus provided by another aspect of the present invention includes an image display apparatus, an imaging optical system and a hologram screen. The hologram screen is arranged to reflect light from a point light source so as to form a point image at a position different from the point light source; and the imaging optical system is arranged to adjust a focus in a vertical direction of an image displayed on the image display apparatus to coincide with the hologram screen. The above-described object is accomplished by such a feature.
In one embodiment, the formed point image is a real image.
In another embodiment, the formed point image is a false image formed at a position on an opposite side of the point light source with respect to the hologram screen.
In one embodiment, the imaging optical system has independent imaging functions in a vertical direction and in a lateral direction. For the vertical direction, a focus in the vertical direction of an image displayed on the image display apparatus is adjusted to coincide with the hologram screen; and for the lateral direction, a focal distance is arranged to be variable.
The above-described optical display apparatus may further include polarization glasses whose polarization transmission directions for respective eyes are orthogonal to each other.
According to the present invention, there may be provided an optical display system having a plurality of display units arranged in a lateral direction, wherein each of the plurality of display units is the optical display apparatus of the present invention having the above-described feature.
Moreover, according to the present invention, there may be provided an optical display system having a plurality of display units arranged in a depth direction, wherein each of the plurality of display units is the optical display apparatus of the present invention having the above-described feature.
The image display apparatus may include: a display device selected from an LED, a CRT, a polymer dispersed type liquid crystal panel and an organic EL panel; and a polarization switching device.
Moreover, the polarization switching device may include a ferroelectric liquid crystal panel.